The prior art teaches equipping vehicles with “variable displacement,” “displacement on demand,” or “multiple displacement” internal combustion engines in which one or more cylinders may be selectively “deactivated,” for example, to improve vehicle fuel economy when operating under relatively low-load conditions. Typically, the cylinders are deactivated through use of deactivatable valve train components, such as the deactivating valve lifters as disclosed in U.S. patent publication no. U.S. 2004/0244751 A1, whereby the intake and exhaust valves of each deactivated cylinder remain in their closed positions notwithstanding continued rotation of their driving cams.
Typically, the intake and exhaust valves of each deactivated cylinder are closed so as to trap combustion gases within each such cylinder, whereupon the deactivated cylinders operate as “air springs” to reduce engine pumping losses when the engine is operated with such cylinders in the deactivated state. When vehicle operating conditions are thereafter deemed to require an engine output torque greater than that achievable without the contribution of the deactivated cylinders, as through a heightened torque demand signal, the deactivatable valve train components are returned to their nominal activated state to thereby “reactivate” the deactivated cylinders.
There is a need, however, to determine whether a deactivated cylinder should be periodically reactivated, even when vehicle operating conditions do not otherwise require cylinder reactivation in response, for example, to a greater torque demand signal, in order to maintain the temperature of certain engine components associated with such deactivatable cylinders above respective desired minimum temperatures.